Dry matter intake and production efficiencies of dairy cows rotationally grazing a perennial ryegrass monoculture, a perennial ryegrass-white clover sward, or a multispecies sward.

Achieving high levels of pasture utilization by pasture-based dairy cattle are the cornerstone of profitable grazing systems. Whereas the productivity of such systems is often considered in terms of milk output per cow or per ha, milk production efficiency necessitates that individual animal milk production and pasture DMI are evaluated simultaneously. Increasing feed efficiency has been shown to improve both the economic resilience and environmental efficiency of grazing, and is influenced by an array of plant, grazing management, and animal-related factors. One of the critical factors is chemical nitrogen (N) fertilization. The need to reduce chemical N fertilizer from both an economical and environmental point of view, has led to increased interest in sward diversification. The challenge of maintaining pasture productivity within such requires the successful incorporation of legumes, such as e.g. white clover within perennial ryegrass. Previous studies indicate that perennial ryegrass associated with white clover swards can produce similar pasture DM yields than perennial ryegrass-only swards, and with a reduced requirement for chemical N application. Moreover, as such pastures may be more palatable and digestible, their DMI could be higher than perennial ryegrass-only swards, resulting in improved milk production per cow as has been shown in some studies. More recently, more diverse pastures, called multispecies swards, containing multiple grass species, legumes, and herbs such as plantain or chicory, have also been observed to maintain pasture productivity with lower chemical N applications compared with perennial ryegrass-only swards, while increasing animal DMI and milk production. Such pastures could also improve the resilience of grazing systems due to different growth patterns, deeper roots, and increased nutrient use efficiency. However, contradictory findings are reported in the literature, with some studies observing no effect of perennial ryegrass-legume or multispecies swards on milk production and DMI. These divergent results can be explained by differences in both legume and herb contributions, seasonality, age of sward post-establishment, and because results were obtained from short term experiments. Therefore, the objective of the study cited was to evaluate the effect of sward diversity on individual cow DMI, milk production, and milk production efficiency over an extended period of time.

Three swards were compared: a perennial ryegrass monoculture (PRG), a PRG with white clover (PRGWC), and a multispecies sward (MSS) composed of grasses, legumes, and herbs. The experiment was conducted as a randomized block design, encompassing 56.1 ha divided into 20 blocks. Three herds of 49 dairy cows were created, one for each sward, and were composed of both pure Holstein-Friesian (HF) and HF crossbred with Jersey (JFX) dairy cows. All the cows were distributed among the three treatments according to lactation number, expected calving date, overall Economic Breeding Index, and milk sub-index within each breed. Pasture production and quality, milk production, DMI, and feed conversion efficiency were monitored over a 2-yr period. The pre-grazing herbage yields and daily herbage allowance were similar across sward types. Daily milk yield (MY) was significantly influenced by sward type, with PRG yielding less than both PRGWC and MSS (13.9, 15.5, and 15.5 kg/cow, respectively). Sward type had a significant effect on DMI, with PRG having the lowest DMI (16.3 kg DM/ cow), compared with MSS (18.7 kg DM/cow), which was the highest whereas PRGWC was intermediate (17.5 kg DM/cow). Consequently, feed efficiency was greatest for PRGWC, intermediate for the MSS, and lowest for the PRG. Breed also had a significant effect on MY and composition, with JFX having a lower MY than HF (14.6 and 15.3 kg/cow, respectively) but with increased milk fat (5.31% and 5.72%, respectively) and protein (4.08% and 4.24%, respectively) concentration. Consequently, milk solids (MlS) production was similar for the two breeds. The JFX animals compared with the HF were more feed efficient.

In conclusion: The inclusion of WC in grazing swards proportionally enhanced both MY and DMI, resulting in similar feed efficiency for PRG and PRGWC swards. In contrast, MSS swards resulted in increased DMI and similar milk production to PRGWC, consequently resulting in reduced feed efficiency for cows grazing MSS compared with PRGWC. In comparison to PRG swards receiving high levels of chemical N fertilizer application, both PRGWC and MSS swards resulted in increased cow intake and milk production performance based on reduced N fertilizer, contributing to more sustainable dairy farming practices.